Systems for atomizing and emitting liquids entrained in a liquid-gas stream find extensive use in various applications, notably fire suppression. Examples of such systems and their components are disclosed in U.S. Pat. No. 7,726,408 to Reilly et al. (hereby incorporated by reference), U.S. Pat. No. 7,686,093 to Reilly et al. (hereby incorporated by reference) and U.S. Pat. No. 7,721,811 to Reilly et al. (hereby incorporated by reference).
Such systems require a supply of pressurized gas for atomization and discharge, and the volume of available gas is often limited by practical considerations such as cost, tankage, and compressor volume flow rate. It is conceivable that the available gas may be exhausted during system use, thereby leaving the structure unprotected against re-ignition of the fire, or vulnerable to a second fire, until the system can be recharged with gas.
In one particular example, water based fire control and suppression sprinkler systems may be used to suppress fires which form in the presence of water soluble combustible liquids, such as ethylene oxide. Of particular concern is the suppression of fires which occur in storage facilities, such as within a bunker or tank holding the liquid. Such a system may generally include a plurality of individual sprinkler heads which are mounted within the tank or bunker in the gas space above the liquid level. The sprinkler heads are normally maintained in a closed condition and include a thermally responsive sensing member to determine when a fire condition has occurred within the bunker. Upon actuation of the thermally responsive member or members, the sprinkler heads open, permitting pressurized water at each of the sprinkler heads to freely flow therethrough for extinguishing the fire.
When actuated, traditional sprinkler heads release a spray of fire suppressing liquid, such as water, onto the area of the fire. The water spray, while somewhat effective, has several disadvantages. For example, the water spray exhibits limited modes of fire suppression. The spray, being composed of relatively large droplets providing a small total surface area, does not efficiently absorb heat and therefore cannot operate efficiently to prevent spread of the fire by lowering the temperature of the ambient air around the fire within the bunker. Large droplets also do not block radiative heat transfer effectively, thereby allowing the fire to spread by this mode. The spray furthermore does not efficiently displace oxygen from the ambient air at the liquid surface, nor is there usually sufficient downward momentum of the droplets to overcome the fire plume and attack the base of the fire. For these reasons atomizing systems, as described above, are advantageous in such applications, as they remedy the deficiencies of the simple water spray systems. However, should the atomizing system prematurely exhaust its gas supply, or exhaust its gas supply and have no means for safeguarding against re-ignition of the fire, it would be advantageous to be able to employ a back-up system, which does not suffer from the disadvantage of a limited gas supply for atomization and discharge.
For water soluble flammable liquids, it is further advantageous, once the fire is out, to supply diluting water to the bunker which will change the concentration of the liquid and render it non-flammable. This will prevent the fire from re-igniting. Sprinklers alone typically used in fire suppression systems simply do not have a rate of flow which makes this feature practical when a bunker or tank having a significant volume is considered.
There is clearly a need for a fire suppression system which operates in multiple fire suppression modes and which would be able to effectively fight a fire in atomization mode and also deliver a sufficient quantity of fire suppressing liquid, or other suppressant, such as foam or gas, as a back-up to prevent re-ignition of a fire and provide protection after the atomizing gas supply is exhausted.